Q.Watermelons
What will cause a watermelon while still young to rot on the ends? Also, what will cause a watermelon to split long ways down the melon?

Blossom end rot will cause them to rot on the ends and is usually attributed to a lack of calcium and/or irregular watering. There are a few things you can try for blossom end rot treatment. Water evenly, not too much or too little. Add a low nitrogen fertilizer to the soil. he s for optimal calcium uptake. Add lime to balance the soil’s pH if it is too low, (should be between 6.0 and 6.5). Add some gypsum to the soil for additional calcium. In addition, remove affected fruit and use a calcium rich foliar spray on the plant.
Irregular watering is the cause of watermelon splitting. Watering a few times a week is generally all that you would need. This article will help you: https://www.gardeningknowhow.com/edible/fruits/watermelon/watering-watermelon.htm